This application is based on an incorporates herein by reference Japanese Patent application No. 2000-330537 filed on Oct. 30, 2000, and Japanese Patent Application No. 2001-254689 filed on Aug. 24, 2001.
1. Field of the Invention
The present invention relates to a screw compressor for compressing fluid by the rotation of a pair of rotors (a male rotor and a female rotor) which are engaged with each other and, in particular, to the discharge port of the fluid.
2. Description of the Related Art
A casing for receiving a pair of rotors of a screw compressor has a discharge port through which fluid compressed by the rotation of the rotors is discharged to the outside of a rotor chamber.
The fluid discharged from the discharge port is pulsated with a pressure difference between a compression chamber and a discharge space to cause the vibrations and noises of an air compressor when the fluid is discharged.
A technology disclosed in Japanese Unexamined Patent Publication No. 6-323269 is a technology for reducing vibration and noise of an air compressor. According to this technology, an abrupt increase in the opening area of the discharge port can be reduced by providing a time difference between the instant when a discharge port in a radial direction begins to open and the instant when a discharge port in an axial direction begins to open.
In the technology disclosed in the above patent gazette, however, the opening area of the discharge port is increased suddenly at the instant when the discharge port in a radial direction starts to open and the instant when the discharge port in an axial direction starts to open, so an effect of reducing the pulsation of the fluid is reduced.
The present invention has been made in view of the above problems. Thus, it is an objective of the present invention to provide a screw compressor capable of reducing the pulsation of discharged fluid thereby reducing vibration and noise by smoothly and steadily increasing the discharge opening area of the discharge port. It is a second object of the present invention to provide a screw compressor which will reduce a decrease in pressure just after fluid starts to discharge and reduce an increase in pressure thereafter to further reduce the pulsation caused by the discharging fluid.
To achieve the objective of the present invention, there is provided a screw compressor. The opening shape of a discharge port in a rotor chamber is inside two tip curved lines and coincides with the two tip curved lines at one common point. When fluid compressed in a compression chamber is discharged from the discharge port, an area of the discharge port communicating with the compression chamber gradually increases from the point where the compression chamber coincides with the discharge port. In other words, when the fluid compressed in the compression chamber is discharged from the discharge port, the discharge opening area of the discharge port smoothly increases. This reduces the pulsation of the discharged fluid and thus the vibration and noise generated by the screw compressor.
The opening area of the discharge port in the rotor chamber may be formed in a polygonal shape having a vertex on at least one tip curved line of the two tip curved lines (or point of intersection of the two tipped curved lines) and one side of the discharge side end face of the rotor chamber. Alternatively, the opening shape of the discharge port in the rotor chamber may be formed in a triangular shape having a vertex at a point of intersection of the two tip curved lines and one side on the discharge side end face of the rotor chamber.
The opening shape of the discharge port in the rotor chamber may have a vertex at a point of intersection of the two tip curved lines and may be formed in such a way that the distance between points where the two tip curved lines intersect an imaginary plane perpendicular to the rotating shafts of the rotors increases as the imaginary plane comes near to the discharge end face of the rotor chamber. The opening shape of the discharge port in the rotor chamber may have a vertex at a point of intersection of the two tip curved lines and may be formed in such a way that the rate of change in the distance between points where the two tip curved lines intersect an imaginary plane perpendicular to the rotating shafts of the rotors increases as the imaginary plane comes near to the discharge end face of the rotor chamber. Additionally, the opening area of the discharge port in the rotor chamber may be set at 65% or less of an area surrounded by the two tip curved lines and the discharge side end face of the rotor chamber.
The rate of change may be decreased from certain portions near the discharge side end face of the rotor chamber. In this case, the portions where the rate of change is decreased are provided at the regions of 70% to 80% of the distance of movement in the axial direction of the two tip curved lines between the instant when the fluid starts discharging from the discharge port and the instant when the fluid finishes discharging.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.